LU-10658 utils: check mount_lustre for allocation failure

LU-10658 utils: check mount_lustre for allocation failure

Check if calloc() failed and return an error rather than dereferencing
the NULL pointer.  Found by static analysis.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ie4a5e3341fab1de77990fc99df54cdc562dcab07
Reviewed-on: https://review.whamcloud.com/31400
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>